Possible evidence for secondary degeneration of central nervous system in the pathogenesis of anencephaly and brain dysraphia. A study in young human fetuses.

In an attempt to help elucidate pathogenetically those human cases exemplifying secondary degeneration of the neural tube causing brain dysraphia, macroscopic and histologic observations of two young human fetuses are described. A nine-week-old anencephalic fetus exhibited an absence of spinal cord (amyelia) with retention of neural crest derivatives (dorsal root ganglion cells and thusir processes, and sympathetic ganglia) implying the presence of a neural tube in early gestation. The second, ten-week-old exencephalic case exhibited restricted brain hemorrhage and necrosis of the telencephalon and brain stem amongst otherwise normal brain and spinal cord tissue. These two young fetal cases may represent examples of a previously normal neural tube which has undergone degeneration at a stage where neural crest has already undergone differentiation, and thus distinguishes them from cases of complete dysraphism which probably results from primary degeneration during neurulation.